This invention is directed to a radio frequency transmitting and receiving antenna which has initial high propagation efficiency and remains functional without significant deterioration of propagation characteristics after much of the top portion thereof is blasted away.
A critical part of any radio frequency communication system is the antenna. Both the transmitting and receiving antenna must be operative in order for the system to work. It is desirable for many communication systems to operate even though the antenna is subject to destructive forces. In this nuclear weapons age, a reliable communications system must have antennas which will remain operative after being subjected to the blast effects of high explosive or atomic weapons. One present practice to achieve "hardened" survivable or blast-resistant antennas is to bury them under large overburdens of blast-resistant material such as concrete. While this protects the antenna, the required propagation through the overburden results in a large signal loss, often six to twelve decibels, at each antenna. In the transmitter, the signal loss must be made up by increased transmitting power, which requires significantly larger equipment and significantly more input energy. Thus, both capital and operating costs are increased. Furthermore, the loss through the overburden above the antenna is greater with higher communication frequency. Losses in the very high frequency communication bands are much larger than in the low frequency bands.